Great question! I wrote an article on this for the American Historical Association last year, looking at the statistics of what people with a history undergrad end up doing. I know that you said you were looking at history at the grad level rather than at the undergrad, but I hope this gives you a place to start.

https://www.historians.org/publications-and-directories/perspectives-on-history/april-2017/history-is-not-a-useless-major-fighting-myths-with-data

So, the first thing to note is that the vast majority of people who take history as their undergrad major do not become professional historians. People in STEM fields love using this to cudgel humanities majors, because the career path isn't as obvious as software development or mechanical engineering. But the good thing is that studying history prepares you to do a lot of things, rather than just one.

Many who take history majors end up being lawyers or teachers at the K-12 level, for example. But so too do you get quite a lot of people ending up being in management of businesses-- which makes a certain degree of sense since history degrees prioritize being able to analyze difficult, often qualitative data, being able to construct an argument, being able to see the forest *and* the trees, and write well.

I don't have as much data to back up what people do with masters' in history, so I will have to speak somewhat more anecdotally. It really depends if you are doing this because you absolutely want to get a career in an historical profession or whether you're a bit more ambivalent (I would personally advocate for the ambivalent route-- if you can find something else you really enjoy doing that uses the skills you got in your MA, do it). The history-related fields are either the professoriate for those very few people who can actually get jobs in it these days, or working in museums, libraries, archives, heritage sites, in publishing nonfiction, working as a freelance writer or other fields. None of these are easy professions to get into, but those are some of the roads you can try to go down if you want history to be an explicit part of your professional life.

I'm sorry if this seems a little bit jaded, but I want to ensure that you know it's not a rosy picture to work specifically as a professional historian. That being said, it is a great major if you want to study something fascinating and then use the skills you acquire there in a range of professional careers.

Good luck!

What are the usual career paths for a historian

If you complete your bachelor's, masters and phd, being a academic/professor is the number one choice. you can specialise in museum studies and go into curating. Otherwise, you can write for history publications(media). There is also archaeology if you like that. Also any government heritage board might hire if they are looking for researchers. Thats all i can think of for now. Demand really depends on your location.

Bear in mind that I'm not American and therefore my perspective will not be specialized for someone studying history in the US, but rather try to apply a general review:

What are the usual career paths for a historian?

Academia/docency is probably the main path; there are some room to be filled in archivistics, museology, archeaology, but the bulk of historians are probably teachers of some sort. It's unlikely to get a regular office job working in this field.

What are the usual career paths for a historian?

I feel like most universities expect their students to further procure their academic endeavours, so most likely you'll be incentivized to publish or pursue a Masters or PhD. You might try to make carreer inside museums, but that varies a lot from place to place, if the museum's administration is public or private, how much politics is needed, etc.

Can someone become a somewhat decently respected Historian without a history degree, through lesser singular courses/ his own personal research perhaps?

Eh? I really wanna say yes but realistically no, not really. In all of those years of humankind contemplating the human past and human activity, some great minds have definitely been built from outside the system. That being said, most renowned scholars have undergone classical training, if not in history proper, in at least some related field like classics, geography or sociology. There is obvious value to pursue knowledge in any case, so if you want to study history for yourself I heavily encourage it, but in this day and age it is extremely difficult to make a carreer out of it if not through traditional means.

There are may history-related career fields to choose from. I've starred the ones that usually require PhDs or Masters degrees.

1. Professors and academics* - these jobs are hard to get. They require years of study, good social connections, a solid academic mentor, the right research interests, and a lot of luck. And even if you do land a job, tenure-track positions are hard to get and you may wind up spending a lot of time in low-paid adjunct positions.
2. Primary and secondary school teachers - this usually requires you to get a teaching certificate or credential. If you teach at a private school, you will usually not require a credential, although these schools tend to recruit teachers with advanced degrees. If you choose to teach abroad in a place like China or Korea, some English schools or foreign schools have social studies or history programs that hire foreign teachers.
3. Think tankers* - lots of think tanks hire historians, or researchers with some historical background paired with economics/political science/IR/etc education.
4. Authors and journalists - Popular historians like David McCullough can be full-time writers. Others, like Rick Atkinson work as journalists and write history books on the side.
5. War graves and POW/MIA group employees* - the Commonwealth War Graves Commission and American Battle Monuments Commission, both employ historians. The Pentagon's Defense POW/MIA Accounting Agency also employs archaeologists and historians to look for missing American servicemen from past wars.
6. Government agencies* - Most major government agencies have small in-house museums and historical staffs. The CIA, for example has several historians on staff. The DEA has its own private museum.
7. Official military historians* - in the US, the Army's Center for Military History, the Navy's Historical and Heritage Command, the Air Force Historical Support Division, and the Marine Corps' History and Museums Division all employ professional historians two write official histories. Military educational institutions like West Point and the Command and General Staff College at Fort Leavenworth also hire historians to teach, in many cases these professors are retired or active-duty military personnel. The U.S. Naval Academy has the unique Permanent Military Professor program where active-duty naval officers can choose to spend ost of their career teaching at the academy
8. Non-profits - non-profit groups like the Battlefields Trust hire historians do to research and conduct public outreach
9. Private collections* - many large private collections employ historians/curators to manage and expand the collection.
10. Museum curators* -this may require special museum studies education, on top of advance degrees and language skills. Museums also hire people with historical preservation and conservation skills.
11. Corporate historians* - many major companies have archivists and corporate historians. Firearms companies like Smith & Wesson employ historians who answer questions gun owners have about the pedigree of their guns.
12. Park rangers - The National Park Service hires full-time and seasonal park rangers to interpret and guide visitors to sites like Little Bighorn and Independence Hall.
13. Tour guides and tour operators - Military historical tours and tours of ancient historical sites and old cities are the big ones here. Sometimes doing this has very few barriers to entry and anyone can start doing it. Other times, it is quite difficult to get your foot in the door due to the gatekeeping involved. There are rigorous tests that have to passed to become a Gettysburg tour guide, for example.
14. Historical YouTubers and podcasters - this is a growing field. Relatively few people do it full-time, but it can be a way to make some side cash.